High temperature electrostatic chuck

ABSTRACT

A hot electrostatic chuck having an expansion joint between a chuck body and a heat transfer body. The expansion joint provides a hermetic seal, accommodates differential thermal stresses between the chuck body and the heat transfer body, and/or controls the amount of heat conducted from the chuck body to the heat transfer body. A plenum between spaced apart surfaces of the chuck body and the heat transfer body is filled with a heat transfer gas such as helium which passes through gas passages such as lift pin holes in the chuck body for backside cooling of a substrate supported on the chuck. The heat transfer gas in the plenum also conducts heat from the chuck body into the heat transfer body. The chuck body can be made of a material with desired electrical and/or thermal properties such as a metallic material or ceramic material. The chuck can be used in various semiconductor processes such as plasma etching, chemical vapor deposition, sputtering, ion implantation, ashing, etc. The ability to operate the chuck at temperatures in excess of 200° C. allows it to be used for plasma etching of noble metals such as Pt which require etching at high temperatures to volatilize low volatility etch products.

This application is a divisional of application Ser. No. 09/469,287,filed on Dec. 22, 1999 now U.S. Pat. No. 6,377,437.

FIELD OF THE INVENTION

The invention relates to an electrostatic chuck (ESC) useful forprocessing substrates such as semiconductor wafers. The ESC can be usedto support a semiconductor substrate in a plasma reaction chamberwherein etching or deposition processes are carried out. The ESC isespecially useful for high temperature plasma etching of materials suchas platinum which are not volatile at low temperatures.

DESCRIPTION OF THE RELATED ART

Vacuum processing chambers are generally used for etching and chemicalvapor depositing (CVD) of materials on substrates by supplying anetching or deposition gas to the vacuum chamber and application of an RFfield to the gas to energize the gas into a plasma state. Examples ofparallel plate, transformer coupled plasma (TCP) which is also calledinductively coupled plasma (ICP), and electron-cyclotron resonance (ECR)reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462;4,948,458; and 5,200,232. Vacuum processing chambers are typicallydesigned to meet performance specifications which depend on the processto be carried out therein. Thus, the particular plasma generatingsource, vacuum pumping arrangement and substrate support associated withthe particular processing chamber must be customized or speciallydesigned to meet the performance specifications.

Substrates are typically held in place within the vacuum chamber duringprocessing by substrate holders. Conventional substrate holders includemechanical clamps and electrostatic clamps (ESC). Examples of mechanicalclamps and ESC substrate holders are provided in commonly owned U.S.Pat. Nos. 5,262,029 and 5,671,116. Substrate holders in the form of anelectrode can supply radiofrequency (RF) power into the chamber, asdisclosed in U.S. Pat. No. 4,579,618.

Substrates including flat panel displays and smaller substrates can becooled by the substrate holder during certain processing steps. Suchcooling is performed by the application of an inert gas, such as helium,between the substrate holder and the opposed surface of the substrate.For instance, see U.S. Pat. Nos. 4,534,816, 5,160,152; 5,238,499; and5,350,479. The cooling gas is typically supplied to channels or apattern of grooves in the substrate holder and applies a back pressureto the substrate. Electrostatic chucks of the monopolar type utilize asingle electrode. For instance, see U.S. Pat. No. 4,665,463.Electrostatic chucks of the bipolar type utilize mutual attractionbetween two electrically charged capacitor plates which are separated bya dielectric layer. For instance, see U.S. Pat. Nos. 4,692,836 and5,055,964.

Substrate supports for vacuum processing chambers are typically mountedon a bottom wall of the chamber making servicing and replacement of thesubstrate support difficult and time consuming. Examples of such bottommounted substrate supports can be found in U.S. Pat. Nos. 4,340,462;4,534,816; 4,579,618; 4,615,755; 4,948,458; 5,200,232; and 5,262,029. Acantilevered support arrangement is described in commonly owned U.S.Pat. Nos. 5,820,723 and 5,948,704.

High temperature electrostatic chucks incorporating clamping electrodesand heater elements have been proposed for use in chemical depositionchambers. See, for example, U.S. Pat. Nos. 5,730,803; 5,867,359;5,908,334; and 5,968,273 and European Patent Publication 628644 A2. Ofthese, EP'644 discloses an aluminum nitride chuck body having an RFmetallic electrode plate which is perforated with holes to form a meshand a heater embedded therein, the chuck body being supported on analumina cylinder such that the outer periphery of the chuck body extendsbeyond the cylinder. The '803 patent discloses a chuck body of siliconnitride or alumina having an electrical grid of Mo, W, W—Mo and a Moheater coil wire embedded therein, the chuck body being supported by aMo heat choke cylinder which surrounds a Cu or Al water cooled coolingplate in thermal contact with the chuck body by a thermal grease whichallows differential expansion between the chuck body and the coolingplate. The '359 patent describes a chuck operational at temperatures onthe order of 500° C., the chuck including sapphire (single crystalAl₂O₃) layers brazed to opposite sides of a niobium electrode and thatassembly brazed to a metal base plate. The '334 patent describes a chuckfor use at temperatures in excess of 175° C., the chuck includingpolyimide films on either side of a monopolar or bipolar electrode withthe lower polyimide film self adhered to a stainless steel platen. The'273 patent discloses a layered chuck body including an aluminum nitridetop layer, an electrode, an aluminum nitride layer, a metal plate, aheater, a metal plate and an aluminum composite, the chuck body beingsupported by a cylinder such that the outer periphery of the chuck bodyextends beyond the cylinder.

Some ESC designs use a heat conduction gas such as helium to enhanceconduction of heat between adjacent surfaces of the wafer support. Forinstance, U.S. Pat. No. 5,155,652 describes an ESC having layersincluding an upper pyrolytic boron nitride layer or optionallypolyimide, alumina, quartz, or diamond, an electrostatic pattern layercomprised of a boron nitride substrate and a conductive pattern ofpyrolytic graphite thereon, a heater layer comprised of a boron nitridesubstrate and a conductive pattern of pyrolytic graphite thereon, and aheat sink base of KOVAR™ (NiCoFe alloy with 29% Ni, 17% Co and 55% Fe).The heat sink base includes water cooling channels in a lower portionthereof and chambers in an upper surface thereof which can be maintainedunder vacuum during heatup of the chuck or filled with helium to aid incooling of a wafer supported by the chuck. U.S. Pat. No. 5,221,403describes a support table comprised of an upper member which supports awafer and a lower member which includes a liquid passage for temperaturecontrol of the wafer, the upper member including an ESC constituted by acopper electrode between polyimide sheets and a gap between contactingsurfaces of the upper and lower members being supplied a heat conductiongas. Commonly owned U.S. Pat. No. 5,835,334 describes a high temperaturechuck wherein helium is introduced between contacting surfaces of alower aluminum electrode and an electrode cap which is bolted to thelower electrode, the electrode cap comprising anodized aluminum ordiamond coated molybdenum. A protective alumina ring and O-ring sealsminimize leakage of the coolant gas between the electrode cap and thelower electrode. The electrode cap includes liquid coolant channels forcirculating a coolant such as ethylene glycol, silicon oil, FLUORINERT™or a water/glycol mixture and the lower electrode includes a heater forheating the chuck to temperatures of about 100-350° C. To preventcracking of the anodization due to differential thermal expansion, theelectrode cap is maintained at temperatures no greater than 200° C. Inthe case of the diamond coated molybdenum electrode cap, the chuck canbe used at higher temperatures.

International Publication WO 99/3696 describes a process for plasmaetching a platinum electrode layer wherein a substrate is heated toabove 150° C. and the Pt layer is etched by a high density inductivelycoupled plasma of an etchant gas comprising chlorine, argon andoptionally BCl₃, HBr or mixture thereof. U.S. Pat. No. 5,930,639 alsodescribes a platinum etch process wherein the Pt forms an electrode of ahigh dielectric constant capacitor, the Pt being etched with an oxygenplasma.

Although there has been some attempts to provide improved chuck designsfor use at high temperatures, the high temperatures impose differentialthermal stresses which are detrimental to use of materials of differentthermal expansion coefficients. This is particularly problematic inmaintaining a hermetic seal between ceramic materials such as aluminumnitride and metallic materials such as stainless steel or aluminum. Assuch, there is a need in the art for improved chuck designs which canaccommodate the thermal cycling demands placed upon high temperaturechuck materials.

SUMMARY OF THE INVENTION

The invention provides an electrostatic chuck useful in a hightemperature vacuum processing chamber comprising a chuck body, a heattransfer body and an expansion joint therebetween. The chuck bodycomprises an electrostatic clamping electrode and optional heaterelement, the electrode being adapted to electrostatically clamp asubstrate such as a semiconductor wafer on an outer surface of the chuckbody. The heat transfer body is separated from the chuck body by aplenum located between spaced apart surfaces of the chuck body and theheat transfer body, the heat transfer body being adapted to remove heatfrom the chuck body by heat conductance through a heat transfer gas inthe plenum. The expansion joint attaches an outer periphery of the chuckbody to the heat transfer body, the expansion joint accommodatingdifferential thermal expansion of the chuck body and the heat transferbody while maintaining a hermetic seal during thermal cycling of thechuck body.

According to a preferred embodiment, the heat transfer body comprises acooling plate having at least one coolant passage therein in whichcoolant can be circulated to maintain the chuck body at a desiredtemperature and the plenum is an annular space extending over at least50% of the underside of the chuck body. In this embodiment, the heattransfer body includes a gas supply passage through which heat transfergas flows into the annular space. According to a preferred embodiment,the chuck body includes gas passages extending between the plenum andthe outer surface of the chuck body. The gas passages can be provided inany suitable arrangement. For instance, if the outer portion of thechuck body tends to become hotter than the central portion thereof, thegas passages can be located adjacent to the expansion joint so that theheat transfer gas flows from the plenum to the underside of an outerperiphery of the substrate during processing thereof.

According to the preferred embodiment, the chuck body comprises ametallic material such as aluminum or alloy thereof or a ceramicmaterial such as aluminum nitride. In the case of a ceramic chuck body,the expansion joint can comprise a thin metal section brazed to theceramic chuck body. Lift pins can be used to raise and lower asubstrate. For instance, the heat transfer body can include lift pinssuch as cable actuated lift pins mounted thereon, the lift pins beingmovable towards and away from the chuck body such that the lift pinstravel through holes in the chuck body to raise and lower a substrateonto and off of the chuck body.

The expansion joint can include a mounting flange adapted to attach tothe heat transfer body and a heat choke such as a single or multi-pieceflexible metal part. The heat choke can include inner and outer annularsections interconnected by a curved section, the inner annular sectionbeing attached to the chuck body and the outer annular section beingattached to the mounting flange. The expansion joint can also include aconnecting member such as a thin ring attached at one end to an outerperiphery of the chuck body by a joint such as a mechanical joint ormetallurgical joint such as a brazed joint, the connecting member beingof a metal having a coefficient of thermal expansion close enough tothat of the chuck body to prevent failure of the joint during thermalcycling of the chuck body. Further, the expansion joint can include athermal expansion section which abuts an outer edge of the chuck body,the thermal expansion section being thermally expandable andcontractible to accommodate changes in dimensions of the chuck body.

The chuck body can include a ceramic or metallic tubular sectionextending from a central portion of the underside of the chuck body suchthat an outer surface of the tubular section defines a wall of theplenum, the tubular section being supported in floating contact with theheat transfer body with a hermetic seal therebetween. The interior ofthe tubular section can include power supplies supplying RF and DC powerto the clamping electrode and AC power to the heater element, and/or atemperature measuring arrangement for monitoring temperature of thechuck body.

According to an embodiment of the invention, the chuck is a replaceableelectrostatic chuck for a vacuum processing chamber wherein the chuckincludes a chuck body and an expansion joint. The chuck comprises anelectrode having an electrical contact attachable to an electrical powersupply which energizes the electrode sufficiently to electrostaticallyclamp a substrate on an outer surface of the chuck body. The expansionjoint includes a first portion attached to an outer periphery of thechuck body and a second portion removably attachable to a heat transferbody such that a plenum is formed between spaced apart surfaces of thechuck body and the heat transfer body.

The invention also provides a method of processing a substrate in avacuum process chamber wherein the substrate is electrostaticallyclamped on a chuck body comprising a clamping electrode and an expansionjoint attaching an outer periphery of the chuck body to a heat transferbody such that a plenum is formed between spaced apart surfaces of thechuck body and the heat transfer body, the method comprising clamping asubstrate on an outer surface of the chuck body by energizing theelectrode, supplying a heat transfer gas to the plenum, the heattransfer gas in the plenum passing through gas passages in the chuckbody to a gap between an underside of the substrate and the outersurface of the chuck body, removing heat from the chuck body by heatconductance through the heat transfer gas supplied to the plenum, andprocessing the substrate.

According to a preferred embodiment, the method further comprisessupplying process gas to the chamber and energizing the process gas intoa plasma and etching an exposed surface of the substrate with the plasmaduring the processing step. However, an exposed surface of the substratecan be coated during the processing step. The process gas can beenergized into the plasma by any suitable technique such as supplyingradiofrequency energy to an antenna which inductively couples theradiofrequency energy into the chamber. During the processing step, thesubstrate can be heated by supplying power to a heater element embeddedin the chuck body. Prior to clamping the substrate, the substrate can belowered onto the outer surface of the chuck body with lift pins mountedon the heat transfer body, the lift pins passing through openings in anouter portion of the chuck body. In order to withdraw heat from thechuck body, the method can include circulating a liquid coolant in theheat transfer body. Temperature changes in the substrate can bemonitored with a temperature sensor supported by the heat transfer bodyand extending through a hole in the chuck body. In the case of plasmaetching a layer of platinum during the processing step, the substratecan be heated to a temperature of over 200° C.

According to the method, it is possible to achieve a desired heatdistribution across the chuck body by removing heat from the chuck bodythrough multiple heat paths. Further, it is possible to adjust theamount of heat removed through these heat paths by changing the pressureof the heat transfer gas in the plenum. For instance, since the ceramicor metallic tubular extension at a central portion of the underside ofthe chuck body conducts heat from the chuck body to the heat transferbody, the method can include adjusting pressure of the heat transfer gasin the plenum so that heat removed through a first heat path provided bythe heat transfer gas in the plenum balances heat removed through asecond heat path provided by the expansion joint and heat removedthrough a third heat path provided by the tubular extension.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings in which like elements bear like referencenumerals, and wherein:

FIG. 1 shows a cross-section of a vacuum processing chamber in which aHTESC assembly of the present invention can be implemented;

FIG. 2 shows a cross-section of another processing chamber in which theHTESC assembly of the present invention can be implemented;

FIG. 3 shows a perspective view of the cantilevered substrate support ofFIG. 2;

FIG. 4 shows a cross-section of a HTESC assembly of a first embodimentof the present invention;

FIG. 5 shows details of a portion of the HTESC assembly shown in FIG. 4;

FIG. 6 shows an enlarged view of a portion of the chuck body shown inFIG. 5;

FIG. 7 shows a cross-section of a HTESC assembly of a second embodimentof the present invention;

FIG. 8 shows details of a portion of the HTESC assembly shown in FIG. 6;and

FIG. 9 shows a cross-section of a portion of a HTESC in accordance witha third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides an electrostatic chuck useful for clampingsubstrates such as semiconductor wafers during processing thereof in avacuum processing chamber such as a plasma etch reactor. Theelectrostatic chuck, however, can be used for other purposes such asclamping substrates during chemical vapor deposition, sputtering, ionimplantation, resist stripping, etc.

According to a preferred embodiment of the invention, the chuck includesa is clamping electrode and an optional heating element which can beused to maintain the substrate supported on the chuck at elevatedtemperatures above 80° C. (the upper limit of certain conventionalchucks is 60° C.), preferably over 200° C., for example 250 to 500° C.For example, the chuck can be used to support a wafer during chemicalvapor deposition or plasma etching of materials wherein it is necessaryto heat the substrate to temperatures on the order of about 150° C. andabove. In order to achieve such high temperatures without damage to thechuck, the chuck includes an expansion joint design which provides thechuck with high temperature functionality in a small package.

According to the preferred embodiment, the expansion joint creates aplenum between spaced apart surfaces of an actively heated portion ofthe chuck and an actively cooled portion of the chuck. The plenum isfilled with a heat transfer gas to conduct heat from the heated portionto the cooled portion of the chuck. With this arrangement, it is notnecessary to use any elastomer seals in the heated portion of the chuck,thereby allowing the heated portion of the chuck to operate attemperatures above which elastomer seals would break down. Also, becauseof the plenum and a heat choke portion of the expansion joint, thecooled portion of the chuck can be maintained at a low enoughtemperature to permit use of low cost elastomer seals in contact withsurfaces of the cooled portion of the chuck. Moreover, the expansionjoint design provides a small overall height of the chuck which makesthe chuck compatible with tight system packaging requirements(footprint). A further advantage of the expansion joint is that thermalstresses can be accommodated between the heated and cooled portions ofthe chuck. In addition, a heat transfer gas such as helium can besupplied to targeted locations on the underside of the substrate withoutthe need for a complicated arrangement of gas passages inside the chuck.

According to a preferred method of using the chuck according to theinvention, a low volatility etch product can be removed from a substrateby a plasma etch process wherein the substrate is heated by the chuck.Such low volatility etch products can be formed during plasma etching ofnoble metals such as Pt, Pd, Ru and Ir, materials under considerationfor the electrodes of capacitors using high-k dielectric materials. Suchlow volatility etch products remain on the substrate surface unless thesubstrate is heated sufficiently. For example, platinum chloride formedduring etching of platinum can be volatilized by heating the substrateto around 300° C. Conventional chucks used in low temperature etchprocesses are unsuited for such high temperature environments since theycan undergo damaging thermal cycling which ruptures hermetic sealsand/or causes failure of chuck materials. Further, because the watercooled portions of such chucks are in direct thermal contact with theheated portion of the chuck, the heat from the chuck can cause thecooling fluid to boil and result in uneven cooling of the chuck and/orinsufficient cooling of the chuck. The chuck according to the inventionsolves these problems through use of the expansion joint design.

According to a preferred embodiment, the chuck body is made from ametallic or ceramic material having desired electrical and/or thermalproperties. For example, the chuck body can be made of aluminum or analuminum alloy. Alternatively, the chuck body can be made from one ormore ceramic materials including nitrides such as aluminum nitride,boron nitride and silicon nitride, carbides such as silicon carbide andboron carbide, oxides such as alumina, etc. with or without fillers suchas particles in the form of whiskers, fibers or the like or infiltratedmetals such as silicon. A ceramic chuck body can be formed by varioustechniques. For instance, the ceramic material can be formed into amonolithic body by a powder metallurgical technique wherein ceramicpower is formed into a chuck body shape such as by compacting or slipcasting the powder with the clamping electrode, heater and power supplyconnections embedded therein, the chuck body being densified bysintering the powder. Alternatively, the chuck body can be formed fromsheets of ceramic material which are overlaid with electricallyconductive patterns for the clamping electrode, the heater and powerfeedthroughs incorporated therein, the layers being cofired to form thefinal chuck body.

Two embodiments of a high temperature electrostatic chuck (HTESC)assembly according to the invention are now described with reference toFIGS. 1-9. The HTESC assembly offers advantageous features such as hightemperature functionality, relatively low power requirements, longeroperational life, simple backside cooling, lower manufacturing cost andcompact design.

The HTESC according to the invention can offer better high temperaturefunctionality and relatively low power requirements compared toconventional chuck assemblies wherein a cooling plate is integrated as aone-piece electrostatic chuck. In such conventional chuck arrangements,the maximum operational temperature is limited to approximately 60° C.In order to increase the maximum operational temperature, the HTESC ofthe present invention has been designed as a two-piece assembly,including an ESC portion such as a ceramic chuck body having anelectrostatic clamping electrode embedded therein and a heat transferbody such as a cooling plate. In addition, an expansion joint in theform of heat break tubulations have been integrated into the ESC portionfor thermally isolating the ESC portion from the cooling plate. The heatbreak tubulations significantly reduce conduction of heat from aperipheral edge of the ESC portion to the cooling plate, therebyallowing the ESC portion to reach temperatures as high as approximately500° C. without requiring the supply of a relatively large amount ofpower to a heater element embedded in the chuck body.

The expansion joint provides a long operational life of the HTESC. Inparticular, by use of the heat break tubulations, the ESC portion canundergo extensive thermal expansion without damaging other parts of theHTESC. The heat break tubulations can be designed as a one-piece metalpart or a multi-piece welded or brazed assembly which includes one ormore thin-walled sections which allow thermal expansion and contractionof the ESC portion while minimizing heat transfer from the ESC portionto the cooling plate. The heat break tubulations accommodatedifferential thermal expansion between the ESC portion and the coolingplate, thereby minimizing stresses within the HTESC assembly and thusreducing the chance of premature failure of the HTESC assembly.Furthermore, the heat break tubulations can be designed in a mannerwhich reduces stress at brazed joints within the HTESC assembly.

Compared to conventional chuck assemblies which rely on a complicatedgas distribution arrangement inside the ESC portion to adequately coolthe substrate, the HTESC according to the present invention includes asimple arrangement which can selectively target portions of thesubstrate where more cooling is desired. For instance, the HTESCassembly includes a plenum between the ESC portion and the cooling plateand the plenum can serve the dual function of (1) withdrawing heat fromthe ESC portion by supplying a heat transfer gas to the plenum and (2)distributing heat transfer gas to select portions of the substratethrough gas passages extending from the plenum to the outer surface ofthe ESC portion. In a HTESC used for plasma etching, gas distributionholes can be provided near the outer periphery of the ESC portion toenhance the cooling of the outer portion of the substrate. Thus, acomplicated gas distribution arrangement is not necessary since the gasdistribution holes can be formed by holes at desired locations in thesupport surface of the ESC portion.

Compared to high temperature chuck assemblies which utilize expensivemetal seals and/or welded bellows arrangements to provide vacuum seals,the use of the expansion joint in the HTESC assembly of the presentinvention can reduce manufacturing costs and/or simplify manufacture ofthe HTESC. In particular, because the heat break tubulations thermallyisolate the hot ESC portion from the cooling plate, standard low costelastomer seals can be used at locations in contact with the coolingplate.

The HTESC according to the invention is designed to provide a smalloverall height so that it can be used in vacuum chambers wherein thechuck is supported on a cantilevered support arm. For example, FIGS. 1-3illustrate examples of vacuum processing chambers 10, 24 into which theHTESC assembly of the present invention could be mounted. While theinvention will be explained with reference to the chamber design shownin FIGS. 1-3, it will be appreciated by those skilled in the art thatthe HTESC assembly of the present invention can be used in any vacuumprocessing chamber wherein it is desired to electrostatically clamp asubstrate. For-example, the HTESC assembly of the present inventioncould be used as part of a substrate support in processing chamberswhere various semiconductor plasma or non-plasma processing steps suchas etching, deposition, resist stripping, etc. can be performed.

As shown in FIG. 1, the vacuum chamber 10 includes a cantileveredsubstrate support 12 extending inwardly from a sidewall of the chamberand a HTESC 14 is supported by the support. A service passage 18containing service conduits (not shown) opens into an interior of thesupport housing 16. The service conduits can be used to service theHTESC, e.g., supply DC power to a clamping electrode, supply RF power tothe clamping electrode or a separate electrode which provides an RF biasto the substrate during processing thereof, supply AC power to a heaterelement, house cables for actuating lift pins, supply coolant forcooling the HTESC and/or the substrate, transmit electrical signals fromsensors or monitoring equipment, etc.

In the embodiment shown, a mounting flange 20 and support arm 22 form anintegral piece which can be removably mounted in an opening in thechamber, e.g., by mechanical fasteners with an O-ring and RF shieldinginterposed between opposed surfaces of the flange 20 and the chamber. Inthe arrangement shown in FIG. 1, gas within the chamber can be withdrawnthrough an opening 21 by a vacuum pump 23. Plasma can be generated inthe chamber by a source of energy (not shown) mounted at the top of thechamber. That is, the top of the chamber is designed to support varioustypes of plasma generating sources such as capacitive coupled, inductivecoupled, microwave, magnetron, helicon, or other suitable plasmagenerating equipment. Also, process gas can be supplied to the chamberby various types of gas supply arrangements such as a gas distributionplate (showerhead), one or more gas rings and/or gas injectors, or othersuitable arrangement.

FIG. 2 illustrates a vacuum processing chamber 24 and a cantileveredsubstrate support 26 on which a chuck assembly 28 has been mounted. Asshown, a substrate 30 is supported on a HTESC assembly 28 mounted on asubstrate support 26. The substrate support 26 is at one end of asupport arm 32 (shown in FIG. 3) mounted in a cantilever fashion suchthat the entire substrate support/support arm assembly 26/32 can beremoved from the chamber by passing the assembly through an opening (notshown) in the sidewall of the chamber 24. Process gas can be supplied tothe chamber by any suitable arrangement such as a gas supply pipe 34 ora gas distribution plate 36 and the gas can be energized into a plasmastate by an antenna 38 such as a planar coil which inductively couplesRf energy through a dielectric member 40. The antenna can be supplied RFenergy by any suitable arrangement such as a conventional RF powergenerator 42 and a match network 44. During processing of a wafer, aheat transfer gas such as helium can be supplied to the backside of thewafer through holes 46, as shown in FIG. 3.

In the chambers shown in FIGS. 1-3, it is desirable to minimize theheight of the HTESC to allow easy removal of the substrate support 26including the HTESC from the chambers 10, 24. Details of how the HTESCcan be made in a compact design will now be explained with reference tothe embodiments shown in FIGS. 4-9.

FIG. 4 shows a HTESC assembly 50 according to a first embodiment of thepresent invention wherein the HTESC assembly 50 is mounted on acantilevered substrate support 52 in a vacuum processing chamber, asdiscussed above with reference to FIGS. 1-3. The HTESC assembly 50 is atwo-piece design including a chuck body 56 and a heat transfer body 58.The chuck body 56 includes a clamping electrode 60, an optional heaterelement 62, an expansion joint 64, and a central tubular extension 66.The expansion joint 64 includes an annular mounting flange 68 which isremovably attached to the heat transfer body 58 by bolts 70. The chuckbody 56 is preferably made of a ceramic material exhibiting dielectricproperties such as aluminum nitride. The expansion joint 64 and the heattransfer body 58 can be made of heat conducting metals such as aluminum,copper, titanium and alloys thereof, but a preferred material is a lowheat conducting metal such as stainless steel, cobalt, nickel,molybdenum, zirconium or alloys thereof. Alternatively, the expansionjoint 64 and the heat transfer body can be made of any materialscompatible in a vacuum chamber in which semiconductor substrates areprocessed.

The heat transfer body includes coolant passages and coolant such aswater or other coolant can be supplied to the passages 72 by suitableconduits one of which is shown at 74. Electrical power can be suppliedto the clamping electrode 60 and the heater element 62 by power supplylines in tubular extension 66. For instance, RF and DC power can besupplied to the clamping electrode by a rod 67, the bottom of which isconnected to a strap 69. Temperature of the chuck body can be monitoredwith a temperature feedback assembly 71 in the tubular extension 66.

A plenum 80 is provided between spaced apart surfaces 82 and 84 of thechuck body 56 and the heat transfer body 58. A heat transfer gas such ashelium can be supplied to the plenum 80 by a gas conduit 76. Thetemperature of the substrate on the chuck body can be monitored with afiberoptic element 77 supported in a fitting 78. Although any type oflift pin assembly can be used such as a pneumatically actuated lift pinassembly, according to a preferred embodiment a fitting mounted in abore 79 can be used to support a cable actuated lift pin assembly.Elastomer seals 88 and 90 fitted in grooves in the heat transfer body 58and an elastomer seal 89 fitted in a collar 91 surrounding tubularextension 66 provide vacuum seals between the expansion joint 64 and theheat transfer body 58 and between the tubular extension 66 and the heattransfer body 58. An elastomer seal 92 provides a vacuum seal between anunderside of the heat transfer body 58 and a dielectric mounting plate94 and an elastomer seal 96 provides a vacuum seal between an undersideof the mounting plate 94 and the housing 54. A dielectric edge ring 98(e.g., alumina, silicon nitride, quartz, etc.) overlies the mountingplate 94 and a dielectric focus ring 100 (e.g., alumina, siliconnitride, silicon carbide, etc.) overlies the edge ring 98 and surroundsthe chuck body 56.

FIG. 5 shows details of the chuck body 56 with the expansion joint 64attached thereto and FIG. 6 is an enlarged view of a brazed joint(detail VI in FIG. 5) between the chuck body 56 and the expansion joint64. As shown in FIG. 5, the expansion joint 64 includes the mountingflange 68, an outer annular section 102, and an inner annular section104, the outer section 102 being connected to the flange 68 by a curvedsection 101 and the inner section 104 being connected to the outersection 102 by a curved section 106. The outer section 102 is separatedfrom the flange 68 by an annular space 108 and the inner section 104 isseparated from the outer section 102 by an annular space 110. The flange68, the outer section 102 and the inner section 104 can be formed (e.g.,machined, cast, forged, etc.) out of a single piece of metal such asstainless steel. Alternatively, the expansion joint can be made from amulti-piece welded or brazed assembly.

The expansion joint can also include a thin metal ring 112 which iswelded at its bottom to the bottom of the inner section 104 and brazedat its top to the underside of the chuck body 56. For added jointstrength, a small ceramic ring 114 can be brazed to adjoining surfacesof the chuck body and the ring 112. If aluminum nitride is chosen forthe chuck body, the ring 112 can be of a NiCoFe alloy such as KOVAR™which has a similar coefficient of thermal expansion as aluminumnitride. As shown in FIG. 6, a small gap 116 (e.g., 0.002-0.004 inch) islocated between an inner surface 120 of the inner section 104 and anouter sidewall 122 of the chuck body 56. The ceramic ring 114 is setback from the sidewall 122 such that a gap 118 is provided between thering 112 and the inner section 104, the gap providing sufficient area toaccommodate a brazed joint 124 between the ring 112 and the underside ofthe chuck body 56. If desired, the brazed joint can be replaced with amechanical joint.

When the chuck body 56 heats up and expands, the sidewall of the chuckbody 56 presses against the inner section 104 and elastically deflectsthe inner and outer sections of the expansion joint. As a result,bending of the ring 112 and consequent stress on the brazed joint 124can be minimized. Likewise, less stress is placed on the welded jointbetween the ring 112 and the inner section 104. Instead, the curvedsections 106 and 110 allow elastic deflection of the inner and outersections of the expansion joint to accommodate thermal expansion andcontraction of the chuck body 56.

FIG. 7 shows a HTESC assembly 50′ according to a second embodiment ofthe present invention wherein the HTESC assembly 50′ is mounted on acantilevered substrate support 52 in a vacuum processing chamber, asdiscussed above with reference to FIGS. 1-3. The HTESC assembly 50′ is atwo-piece design including a chuck body 56′and a heat transfer body 58′.The chuck body 56′ includes a clamping electrode 60′, an optional heaterelement 62′, an expansion joint 64′, and a central tubular extension66′. The expansion joint 64′ includes an annular mounting flange 68′which is removably attached to the heat transfer body 58′ by bolts 70.The chuck body 56′ is preferably made of a ceramic material exhibitingdielectric properties such as aluminum nitride. The expansion joint 64′and the heat transfer body 58′ can be made of heat conducting metalssuch as aluminum, copper, titanium and alloys thereof, but a preferredmaterial is a low heat conducting metal such as stainless steel, cobalt,nickel, molybdenum, zirconium or alloys thereof. Alternatively, thechuck body 56′, the expansion joint 64′ and the heat transfer body canbe made of any materials compatible in a vacuum chamber in whichsemiconductor substrates are processed.

The heat transfer body 58′ includes coolant passages 72 and coolant suchas water or other coolant can be supplied to the passages 72 by conduitsone of which is shown at 74. Electrical power can be supplied to theclamping electrode 60′ and the beater element 62′ by power supply linesin tubular extension 66′. For instance, RF and DC power can be suppliedto the clamping electrode by a rod 67′, the bottom of which is connectedto a strap 69′. Temperature of the chuck body can be monitored with atemperature feedback assembly 71 in the tubular extension.

A plenum 80 is provided between spaced apart surfaces 82 and 84 of thechuck body 56′ and the heat transfer body 58′. A heat transfer gas suchas helium can be supplied to the plenum 80 by a gas conduit 76. Thetemperature of the substrate on the chuck body can be monitored with afiberoptic element 77 supported in a fitting 78. Although any type oflift pin assembly can be used such as a pneumatically actuated lift pinassembly, according to a preferred embodiment a fitting mounted in abore 79 can be used to support a cable actuated lift pin. Elastomerseals 88, 89 and 90 fitted in grooves in the heat transfer body 58′ anda casing 59 bolted to the heat transfer body 58′ provide vacuum sealsbetween the expansion joint 64′ and the heat transfer body 58′ andbetween the tubular extension 66′ and the casing 59. An elastomer seal92 provides a vacuum seal between an underside of the heat transfer body58′ and a dielectric mounting plate 94 and an elastomer seal 96 providesa vacuum seal between an underside of the mounting plate 94 and thehousing 54. A dielectric edge ring 98 (e.g., alumina, silicon nitride,quartz, etc.) overlies the mounting plate 94 and a dielectric focus ring100 (e.g., alumina, silicon nitride, silicon carbide, etc.) overlies theedge ring 98 and surrounds the chuck body 56′.

FIG. 8 shows details of the chuck body 56′ with the expansion joint 64′attached thereto. As shown in FIG. 8, the expansion joint 64′ includesthe mounting flange 68′, an outer annular section 102′, and an innerannular section 104′, the outer section 102′ being connected to theflange 68′ by a curved section 101′ and the inner section 104′ beingconnected to the outer section 102′ by a curved section 106′. The outersection 102′ is separated from the flange 68′ by an annular space 108′and the inner section 104′ is separated from the outer section 102′ byan annular space 110′. The flange 68′, the outer section 102′ and theinner section 104′ can be formed (e.g., machined, cast, forged, etc.)out of a single piece of metal such as stainless steel or a multi-piecewelded or brazed assembly of one or more metals such as stainless steel.

The expansion joint 64′ can also include a thin metal ring 112′ whichhas a flange 113 at its bottom welded to a lip of an extension 105 onthe bottom of the inner section 104′. The ring 112′ is brazed at its topto the underside of the chuck body 56′. Alternatively, the ring 112′ canbe mechanically attached to the chuck body. If aluminum nitride ischosen for the chuck body, the ring 112′ can be of a NiCoFe alloy suchas KOVAR™ which has a similar coefficient of thermal expansion asaluminum nitride. A small gap 116 (e.g., 0.002-0.004 inch) is locatedbetween an inner surface 120′ of the inner section 104′ and an outersidewall 122′ of the chuck body 56′.

When the chuck body 56′ heats up and expands, the sidewall 122′ of thechuck body 56′ presses against the surface 120′ of the inner section104′ and elastically deflects the inner and outer sections of theexpansion joint 64′. As a result, bending of the ring 112′ andconsequent stress on the brazed joint at the top of the ring 112′ can beminimized. Likewise, less stress is placed on the welded joint 115between the ring 112′ and the inner section 104′. Instead, the curvedsections 106′ and 110′ allow elastic deflection of the inner and outersections of the expansion joint 64′ to accommodate thermal expansion andcontraction of the chuck body 56′.

FIG. 9 shows another HTESC in accordance with the invention wherein theexpansion joint 64″ includes a single annular thin walled section 126connected to the mounting flange 68″ by a curved section 127 andconnected to the chuck body 56″ by a curved section 128. The section 126is separated from the flange 68″ by an annular space 129. The substratecan be raised and lowered with any suitable lift pin arrangement such asa pneumatically actuated lift pin assembly or a cable actuated assembly.In the embodiment shown, the lift pin assembly includes a plurality ofcable actuated lift pins located at circumferentially spaced apartlocations around the periphery of the chuck body 56″. For instance, aplurality of cable actuated lift pin assemblies 130 can be located closeto the expansion joint 64″, as shown in FIG. 9.

The lift pin assembly 130 includes a lift pin 132 which can be raisedand lowered by a cable (not shown) attached to a slidable lift pinsupport 134 in a housing 136. The housing 136 is fitted in the bore 86′so as to maintain a hermetic seal. A further description of such cableactuated lift pins can be found in commonly owned U.S. Pat. No.5,796,066. The lift pin hole 46′ is sized to allow movement of the pinand heat transfer gas in the plenum 80 can flow around the lift pin 132to the underside of a substrate located in overhanging relationship withthe chuck body 56″.

The heat transfer gas can be supplied to the plenum 80 through a gaspassage 138 and the gas in the plenum can be maintained at any suitablepressure such as 2 to 20 Torr. Depending on the size of the substrate, 3or more lift pins 132 can be used to raise and lower the substrate. Asshown in FIG. 3, additional holes 46 can be provided to evenlydistribute the gas around the edge of the substrate. Further, the holescan open into a shallow groove (not shown) in the upper surface of thechuck body to aid in distributing the gas under the substrate. In orderto provide power to the clamping electrode and the heater element, powersupplies 78′ can be provided in the interior of the tubular extension66″. Also, one of the power supplies 78′ can be used to carry electricalsignals to a substrate temperature sensor (not shown) located in thechuck body 56″.

With the arrangement shown in FIG. 9, the chuck body 56″ can expand whenheated and such expansion can be accommodated by the expansion joint64″. The tubular extension 66″ is supported freely above the heattransfer body 58″ and due to the clamping pressure created by the boltedflange 68″, a hermetic seal is maintained between the tubular extensionand the heat transfer body 68″ by the elastomer seal 90′.

The thin cross-section of the annular section or sections of theexpansion joint allows for the thermal isolation of the chuck body fromthe remainder of the HTESC assembly. By thermally isolating the chuckbody and thereby minimizing heat loss due to heat conduction away fromthe chuck body, the chuck body is capable of reaching temperatures ashigh as approximately 500° C. without requiring the expenditure of arelatively large amount of electrical power. In addition, the shape ofthe expansion joint allows the joint to expand and contract as a resultof thermal cycling during processing of a substrate. Accordingly,because thermal stresses on welded and brazed joints of the HTESCassembly are minmized, the HTESC can be expected to have a long workinglife.

By thermally isolating the chuck body from the rest of the HTESCassembly, standard low cost elastomer materials can be used to formvacuum seals with the heat transfer body. Such vacuum seals can be madefrom a low cost material such as VITON™. The chuck body can be made fromcofired layers of ceramic material and metallization layers. Forexample, commonly owned U.S. Pat. No. 5,880,922 describes a suitabletechnique for making a ceramic chuck body. For example, the layers caninclude a conductive layer forming a monopolar or bipolar electrode(which also functions as a RF bias electrode) sandwiched between ceramiclayers. A heater element such as one or more spiral resistance heatingelements can be located between additional ceramic layers. Variousconductive feedthroughs for supplying power to the clamping electrodeand heater element can also be incorporated in the chuck body.

While the invention has been described in detail with reference topreferred embodiments thereof, it will be apparent to one skilled in theart that various changes can be made, and equivalents employed, withoutdeparting from the scope of the invention.

What is claimed is:
 1. A method of processing a substrate in a vacuumprocess chamber wherein the substrate is electrostatically clamped on achuck body comprising a clamping electrode and an expansion jointattaching an outer periphery of the chuck body to a heat transfer bodysuch that a plenum is formed between spaced apart surfaces of the chuckbody and the heat transfer body, the method comprising: clamping asubstrate on an outer surface of the chuck body by energizing theelectrode; supplying a heat transfer gas to the plenum, the heattransfer gas in the plenum passing through gas passages in the chuckbody to a gap between an underside of the substrate and the outersurface of the chuck body; removing heat from the chuck body by heatconductance through the heat transfer gas supplied to the plenum; andprocessing the substrate.
 2. The method of claim 1, further comprisingsupplying process gas to the chamber, energizing the process gas into aplasma, and etching an exposed surface of the substrate with the plasmaduring the processing step.
 3. The method of claim 2, wherein theprocess gas is energized into the plasma by supplying radiofrequencyenergy to an antenna which inductively couples the radiofrequency energyinto the chamber.
 4. The method of claim 1, wherein an exposed surfaceof the substrate is coated during the processing step.
 5. The method ofclaim 1, further comprising heating the substrate above 100° C. bysupplying power to a heater element embedded in the chuck body.
 6. Themethod of claim 1, further comprising lowering the substrate onto theouter surface of the chuck body with lift pins mounted on the heattransfer body, the lift pins passing through openings in an outerportion of the chuck body.
 7. The method of claim 1, further comprisingcirculating a liquid coolant in the heat transfer body.
 8. The method ofclaim 1, further comprising monitoring temperature changes in thesubstrate with a temperature sensor located in a ceramic or metallictubular section extending from a central portion of the underside of thechuck body, the interior of the tubular section being at atmosphericpressure.
 9. The method of claim 1, wherein the substrate is at atemperature of over 80° C. during the processing step.
 10. The method ofclaim 1, wherein the substrate is at a temperature of over 200° C.during the processing step.
 11. The method of claim 1, wherein a layerof platinum is plasma etched during the processing step.
 12. The methodof claim 1, wherein a ceramic or metallic tubular extension extends froma central portion of the underside of the chuck body and conducts heatbetween the chuck body and the heat transfer body, the method furthercomprising adjusting pressure of the heat transfer gas in the plenum sothat heat removed through a first heat path provided by the heattransfer gas in the plenum balances heat removed through a second heatpath provided by the expansion joint and heat removed through a thirdheat path provided by the tubular extension.